As a general rule, no matter what one classifies as junk food, such foods are perfectly safe to eat, as long as they are integrated into a well balanced diet. There's nothing wrong with having some potato chips now and then, but consuming a diet based primarily on such food is a cause for concern. Because junk food often lacks useful vitamins and minerals, people who eat it exclusively may suffer from nutritional deficiencies that could cause health problems, and they may experience other physical issues like indigestion as a consequence